Wrist assembly for an industrial robot

ABSTRACT

The two-axes wrist assembly of the chain-drive system for an industrial robot has a base wrist unit (12) disposed on one side of the robot arm (11). A hollow shaft (13) is fixed at one end thereof to the base wrist unit and is supported at the same end on one side wall of the free end of the robot arm so as to be rotatable about a first axis (β) intersecting the longitudinal axis of the robot arm at right angles. The other end of the hollow shaft is positioned opposite to the inner surface of the other side wall of the free end of the robot arm. A fore wrist unit (16) is supported on the base wrist so as to be rotatable about a second axis (α) intersecting the first axis at right angles. A through shaft (17) is provided rotatably within and coaxially with the hollow shaft. The fore wrist unit is interlocked with the hollow shaft by a pair of bevel gears (18, 19). A first sprocket (22) is provided on the other end of the hollow shaft coaxially with the same within the free end of the robot arm. A second sprocket (23) is disposed provided on and coaxially with the through shaft adjacent to the first sprocket within the free end of the robot arm. The first and second sprockets engage first an second chains (26, 27) for power transmission, respectively.

DESCRIPTION

1. Technical Field

The present invention relates to a wrist assembly for an industrialrobot, and more particularly, to a two-axes wrist assembly of thechain-drive system.

2. Background Art

Generally, a two-axes wrist assembly provided at the free end of therobot arm of an industrial robot comprises a base wrist unit joined tothe free end of the robot arm so as to be rotatable relative to the freeend of the robot arm about a first axis intersecting the longitudinalaxis of the robot arm at right angles, and a fore wrist unit joined tothe base wrist unit so as to be rotatable relative to the base wristunit about a second axis intersecting the first axis at right angles.The shaft-drive system and the chain-drive system have been well-knowndriving systems for driving the base wrist unit and the fore wrist unitof a wrist assembly of the above-mentioned type. Ordinarily, theshaft-drive system requires many power transmitting parts to transmitthe rotation of two power transmitting shafts extended along thelongitudinal direction of the robot arm through bevel gears to the basewrist unit and the fore wrist unit, which disadvantageously increasesthe total weight of the robot arm and the wrist assembly.

On the other hand, the chain-drive system is able to couple sprocketsengaging chains directly with the base wrist unit, and hence only areduced number of power transmitting parts are necessary and the robotarm and the wrist assembly can be formed in lightweight constructions.

Accordingly, chain-drive wrist assemblies have widely been employedrecently in industrial robots.

A conventional ordinary chain-driven two-axes wrist assembly is shown inFIGS. 1 and 2. Referring to FIGS. 1 and 2, the wrist assembly of thistype has a base wrist unit 2 which is provided, at the opposite sidesthereof, with shafts 2a and 2b. The base wrist unit 2 is supported bythe shafts 2a and 2b so as to be rotatable relative to the robot arm 1about a first axis β intersecting the longitudinal axis of the robot arm1 at right angles. A fore wrist unit 3 is supported on the base wristunit 2 so as to be rotatable about an axis α intersecting the first axisβ at right angles. A first sprocket 4 disposed on one side of the basewrist unit 2. A first chain 5 extended along one side of the robot arm 1is wrapped round the sprocket 4. The other shaft 2b of the base wristunit 2 is a hollow shaft. A shaft 6 supported coaxially with and withinthe hollow shaft 2b extends through the shaft 2b and is connectedthrough a pair of bevel gears 7 and 8 to the fore wrist unit 3. A secondsprocket 9 disposed on the other side of the base wrist unit 2 isattached to the shaft 6. A second chain 10 extended along the other sideof the robot arm 1 is wrapped round the sprocket 9.

The wrist assembly of this constitution requires the chains 5 and 10 tobe extended along the opposite sides of the robot arm 1 so as tocorrespond to the sprockets 4 and 9 disposed on the opposite sides ofthe base wrist unit 2, respectively. Therefore, the thickness of therobot arm needs to be increased in order to accommodate the chains 5 and10 therein, and hence the sizes of the components for supporting therobot arm 1 need to be enlarged. To make the robot arm 1 capable ofmotion about the longitudinal axis thereof, in particular, it is ageneral practice to provide the robot arm 1 with a gear in the form of aflange and to transmit the driving force of a motor to the gear. In sucha case, the enlargement of the thickness of the robot arm 1 entails theenlargement of the diameter of the gear.

Furthermore, since the base wrist unit 2 of the wrist assembly of theabove-mentioned constitution is supported on the opposite sides thereofon the free end of the robot arm 1, the range of motion of the basewrist unit 2 is liable to be restricted by the robot arm 1, whichresults in the degradation of the kinematic functions of the wristassembly.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to provide a compact andlightweight wrist assembly for an industrial robot, capable of beingassociated with a compact and lightweight robot arm and having improvedkinematic functions.

The present invention provides a wrist assembly for an industrial robot,comprising: a base wrist unit disposed on one side of the free end of arobot arm and having a hollow shaft supported on the free end of therobot arm so as to be rotatable relative to the robot arm about a firstaxis intersecting the longitudinal axis of the robot arm at rightangles; a fore wrist unit supported on the base wrist unit so as to berotatable about a second axis intersecting the first axis at rightangles; a through shaft inserted through and coaxially with the hollowshaft so as to be rotatable and connected through bevel gears to thefore wrist unit; and sprockets disposed adjacent to each other withinthe free end of the robot arm to transmit driving forces to the hollowshaft and the through shaft respectively.

The sprockets for transmitting rotative power to the base wrist unit andthe fore wrist unit of the wrist assembly for an industrial robot,according to the present invention, are disposed adjacent to each otherwithin the free end of a robot arm. Therefore, the chains fortransmitting rotative power to the sprockets can be extended adjacent toeach other in the central portion of the robot arm. Accordingly, therobot arm may be a thin robot arm, and hence the respective sizes andweights of the robot arm and the parts of the robot arm supportingmechanism can be reduced. This merit of the present invention isextremely advantageous, particularly in making the robot arm capable ofmotion about the longitudinal axis thereof.

Furthermore, in the wrist assembly according to the present invention,since the base wrist unit is disposed on one side of a robot arm, thebase wrist unit is able to rotate unrestrictedly about the first axisintersecting the longitudinal axis of the robot arm at right angles,without interfering with the robot arm, and hence the range of freedomof motion of the base wrist unit is expanded.

These and other objects and features of the present invention willbecome more apparent from the following detailed description of apreferred embodiment of the present invention taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagrammatic view in section showing aconventional two-axes wrist assembly for an industrial robot;

FIG. 2 is a side elevation of the wrist assembly of FIG. 1;

FIG. 3 is a sectional view of a two-axes wrist assembly for anindustrial robot, in a preferred embodiment according to the presentinvention;

FIG. 4 is a side elevation of the wrist assembly of FIG. 3; and

FIG. 5 is a front elevation of the wrist assembly of FIG. 3.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIGS. 3 to 5, a base wrist unit 12 is disposed on one sideof the free end of the robot arm 11 of an industrial robot. The basewrist unit 12 has a hollow shaft 13 supported on the free end of therobot arm 11 so as to be rotatable in a bearing 14 relative to the freeend of the robot arm 11 about a first axis β intersecting thelongitudinal axis of the robot arm 11 at right angles.

A fore wrist unit 16 is supported on the base wrist unit 12 so as to berotatable in a bearing 15 about a second axis α intersecting the firstaxis β at right angles.

A through shaft 17 is inserted coaxially with and through the hollowshaft 13 so as to be rotatable therein. The through shaft 17 isconnected through a pair of bevel gears 18 and 19 to the fore wrist unit16. The bevel gears 18 and 19 are supported on the base wrist unit 12 soas to be rotatable in bearings 20 and 21, respectively.

A first sprocket 22 for transmitting rotative power to the hollow shaft13 and a second sprocket 23 for transmitting rotative power to thethrough shaft 17 are disposed side by side within the free end of therobot arm 11. In this embodiment, the first sprocket 22 is formedintegrally with the hollow shaft 13, and hence the same is rotatableabout the axis β. The second sprocket 23 is keyed to the through shaft17 and supported on the hollow shaft 13 and the robot arm 11 by bearings24 and 25, respectively, so as to be rotatable about the axis β.

According to the present invention, the sprockets 22 and 23 fortransmitting rotative power to the base wrist unit 12 and the fore wristunit 16 of the wrist assembly, respectively, are disposed adjacent toeach other. Consequently, a first chain 26 and a second chain 27 fortransmitting rotative power to the sprockets 22 and 23, respectively,can be extended adjacent to each other in the central portion of therobot arm 11, and hence the robot arm 11 may be a thin robot arm, whichis extremely advantageous for making the robot arm 11 capable ofkinematic function about the longitudinal axis thereof.

In this wrist assembly, the base wrist unit 12 is disposed on one sideof the robot arm 11. Therefore, the base wrist unit is allowed to rotateover a wide range of rotation, for example, an angular range of 360degrees, about the first axis β without interfering with the robot arm11. Accordingly, the range of motion of the base wrist unit 12 can beexpanded.

Although the present invention has been described hereinbefore withreference to a preferred embodiment thereof, the present invention isnot limited to the above-mentioned embodiment, but may be embodied invarious modifications without departing from the scope of the followingclaims. For example, the first sprocket and the hollow shaft may beformed separately and joined together. Furthermore, it is possible toform the second sprocket integrally with the through shaft and to formthe bevel gear separately from the through shaft.

CAPABILITY OF EXPLOITATION IN INDUSTRY

The wrist assembly according to the present invention is applicable toindustrial robots for various work such as assembling parts, welding,and painting. Since the present invention enables the reduction of thesize and weight of the robot arm as well as those of the wrist assembly,the range of motion of the wrist assembly is expanded, which enables theindustrial robot to work in a narrow space.

We claim:
 1. A wrist assembly for an industrial robot having a hollowrobot arm, said hollow robot arm having at a free end thereof oppositeside walls for defining therebetween an interior of said hollow robotarm, one of said side walls having a through hole extending in adirection perpendicular to a longitudinal axis of said hollow robot arm,said wrist assembly comprising:a base wrist unit disposed outside saidone of said side walls of said hollow robot arm; a hollow shaft fixed atone end thereof to the base wrist unit and inserted through said throughhole of said one of said side walls into said interior of said hollowrobot arm with the other end thereof positioned opposite to the innersurface of another one of said side walls of said hollow robot arm, saidhollow shaft being rotatably supported on an inner surface of saidthrough hole in a first bearing member so as to be rotatable about afirst axis intersecting said longitudinal axis of said hollow robot armat right angles, said hollow shaft rotating said base wrist unit aboutsaid first axis; a fore wrist unit supported on said base wrist unit androtatable about a second axis intersecting said first axis at rightangles; a through shaft inserted coaxially with and through said hollowshaft rotatably supported on an inner surface of said hollow shaft in asecond bearing member, said through shaft rotating said fore wrist unitabout said second axis; a pair of bevel gears disposed within said forewrist unit an interlocking said through shaft with said fore wrist unitfor rotation about said second axis, one of said bevel gears beingformed integrally with said through shaft; a first sprocket formed onsaid other end of and coaxially with said hollow shaft in said interiorof said hollow robot arm and engaging a first chain for powertransmission for rotating said base wrist unit about said first axis;and a second sprocket fixedly fitted on and coaxial with said throughshaft adjacent to said first sprocket within said interior of saidhollow robot arm and engaging a second chain for power transmission forrotating said fore wrist unit about said second axis, said secondsprocket being rotatably supported on the inner surface of said hollowshaft and a cylindrical recess formed in the inner surface of saidanother one of said side walls on third and fourth bearing members,respectively, wherein the respective outside diameters of said first andsecond sprockets and said fourth bearing member are smaller than theinside diameter of said through hole formed in said one of said sidewalls of said hollow robot arm so that said first and second sprocketsand said third bearing member can be inserted into and withdrawn fromsaid interior of said hollow robot arm through said through hole.